3A.1 Has there been an increase in Atlantic basin category 5 hurricane frequency over the past century?

Monday, 24 January 2011: 4:00 PM
608 (Washington State Convention Center)
Andrew B. Hagen, Univ. of Miami/RSMAS, Miami, FL; and C. W. Landsea

A study was conducted to determine the extent to which technological advances and improvements in observational capabilities for monitoring the intensity of extreme tropical cyclones in the Atlantic Basin have evolved over the past century. The official record (HURDAT) for the Atlantic basin has shown an unprecedented increase in the number of Category 5 hurricanes. Several previous studies have stated that there has been an increase in the number of intense hurricanes both in the Atlantic Ocean and globally (e.g. Webster et al. 2005) and attribute this increase to anthropogenic global warming and/or global climate change. Other studies (e.g. Landsea 2007, Landsea et al. 2010) claim that the apparent increased hurricane activity in the record is due to better observational capabilities and improved technology for detecting these intense hurricanes. This study delves deeper into the question of whether the recently observed increase in the number of Category 5 hurricanes in the Atlantic Basin is an artifact of better observations/improved technology or rather possibly due to climate changes.

Ten Category 5 hurricanes were recorded in the Atlantic Basin from 1992-2007 [Hurricane Andrew (1992) to Hurricane Felix (2007)]. A new methodology was developed to determine how many of these ten recent Category 5s would have been recorded as Category 5s if they had occurred during the late 1940s and the early 1950s periods using only the technology and observational practices that were available during those two periods respectively. For example, in the late 1940s, we would not have known that Hurricane Katrina (2005) was a Category 5 in the central Gulf of Mexico because there were no satellites, and aircraft reconnaissance would not perform penetrations of major hurricanes during this period. Since there were no surface observations in 2005 that recorded Category 5 winds or a corresponding pressure value indicative of a Category 5, Hurricane Katrina would have been listed with a peak intensity of only a Category 4 if it had occurred during the late 1940s. The early 1950s (1950-1953) is treated as a separate period from the late 1940s (1944-1949) in this study because it was found (from both literature reviews as well as new research conducted for this study) that aircraft reconnaissance observing techniques underwent some improvements around 1950 compared with the first six years of routine military aircraft reconnaissance. New best track intensities were drawn for the entire lifetime of these ten recent Category 5s (using late 1940s and early 1950s technology along with current reanalysis techniques). It is found that only two of these ten (Andrew of 1992 and Mitch of 1998) would have been recorded as Category 5 hurricanes if they had occurred during the late 1940s period. Research for placing these storms into the period of the early 1950s is still being conducted and will be presented at the conference along with the results of the late 1940s comparison. The results obtained so far suggest that intensity estimates for extreme tropical cyclones during the late 1940s (and likely extending until the beginning of the satellite era) are unreliable.

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